Methods for processing coal

Abstract

Methods of converting raw coals into low ash fuels which are competitive with the heavier grades of petroleum-based fuels and into other products. The raw coal is comminuted in aqueous slurry until resolved into separate, particulate phases of coal and mineral matter. Then, an agglomerating agent is mixed with the slurry until the coal particles have coalesced into agglomerates, and the agglomerates are recovered from the slurry. The ash content of the product coal can be reduced even further by redispersing the product coal in clean water and then reagglomerating the particles of coal and/or by subjecting it to an acid leach.

What is claimed is: 
     
       1. A process of preparing a low ash coal from a composite of coal and mineral matter, said method comprising the steps of: reducing said composite to a particle size distribution such that said composite can be slurried; mixing said composite with an aqueous liquid in an amount sufficient to form a slurry of said composite; comminuting said composite while in said slurry to a size consist such that the composite is resolved into separate particulate phases of coal and hydrophilic mineral matter and said mineral matter is dispersed in the aqueous carrier of the slurry; thereafter mixing with said slurry a liquid agglomerating agent which: has a high interfacial tension with water and a low viscosity, is capable of being adsorbed onto the surfaces of the coal particles to render them more hydrophobic without effecting the hydrophilicity of the mineral matter, and is selected from the group consisting of: 1,1,2-trichloro-1,2,2-trifluoroethane,   pentane   trichlorofluoromethane, and   2-methylbutane; agitating the resulting mixture without more than incidental further comminution of the coal, thereby effecting a separation of said coal particles from said aqueous liquid and the mineral matter dispersed therein and a coalesence of said coal particles into product coal agglomerates; and recovering said agglomerates from said slurry.     
     
     
       2. A process for recovering coal from a composite in which mineral matter is associated therewith, said process including the steps of: comminuting said composite in an aqueous liquid until it is resolved into a first phase consisting of particles which are essentially coal and a second phase consisting of particles which are essentially hydrophilic mineral matter; diluting said slurry; adding to the resulting aqueous slurry of coal and mineral matter an agglomerant which: is capable of being adsorbed onto the surfaces of the coal particles to render them more hydrophobic without effecting the hydrophilicity of the mineral matter and of bonding said coal particles into agglomerates of product coal and is selected from the group consisting of: 1,1,2-trichloro-12,2-trifluoroethane,   pentane,   trichlorofluoromethane, and   2-methylbutane; thereafter subjecting said slurry to agitation without more than incidental further comminution of said coal until the particles of coal have coalesced into agglomerates and the voids between the particles in said agglomerates have been filled with agglomerant to expel water and mineral matter therefrom; and then recovering said agglomerates from the slurry.     
     
     
       3. A process for recovering coal from a composite in which mineral matter is associated therewith, said process including the steps of: comminuting said composite in an aqueous liquid until it is resolved into particles which are essentially coal and particles which are essentially mineral matter; effecting a separation of said coal particles from said mineral matter particles and a coalescence of the coal particles into agglomerates with an agglomerant which: is capable of being adsorbed onto the surfaces of the coal particles to render them more hydrophobic without effecting the hydrophilicity of the mineral matter and of forming liquid bridges between the coal particles and is selected from the group consisting of: 1,1,1-trichloro-1,2,2-trifluoroethane,   pentane,   trichlorofluoromethane, and   2-methylbutane; recovering the agglomerates from the aqueous liquid; introducing the particles making up said agglomerant into an aqueous liquid, reducing the concentration of agglomerant relative to the solids in said liquid to a level sufficient to dissolve said liquid bridges, and agitating the solids and aqueous liquid to thereby effect a dispersion in said aqueous liquid of the coal particles making up said agglomerates and any particles of mineral matter trapped therein to potentiate a separation of the particles of coal and mineral matter; thereafter separating the dispersed coal particles from the dispersed mineral matter particles and effecting a coalesence of the dispersed coal particles with an agglomerant as aforesaid; and recovering the agglomerates thus formed from the aqueous liquid in which the particles were dispersed.   
     
     
       4. A process as defined in any of the preceding claims 1-3 which includes the step of adding to the aqueous liquid in which the composite of coal and mineral matter is comminuted at least one composition which is effective to disperse said composite in said aqueous liquid and thereby promote more efficient comminution of the composite, said composition being a liquid fluorocarbon, an ionic surfactant, or a nonionic surfactant. 
     
     
       5. A process as defined in any of the preceding claims 1-3 wherein said composite is comminuted in said slurry predominantly to a top size of not more than about 30 microns. 
     
     
       6. A process as defined in any of the preceding claims 1-3 wherein said composite is comminuted before said slurry is formed predominantly to a top size of not more than about 250 microns by dry milling. 
     
     
       7. A process as defined in any of the preceding claims 1-3 wherein said slurry is maintained at a pH in the range of 6 to 10 during the comminution of the composite therein. 
     
     
       8. A process as defined in any of the preceding claims 1-3 wherein the ratio of composite to water in the slurry during the comminution of the coal in the slurry is not less than 20 to 70 weight percent. 
     
     
       9. A process as defined in any of the preceding claims 1-3 wherein the mixing of said agglomerant with said slurry is carried out in a separate processing unit from the subsequent dissociation of the coal particles from the aqueous and mineral matter phases of said slurry and agglomeration of the coal particles. 
     
     
       10. A process as defined in any of the preceding claims 1-3 wherein the separation of the coal particles from the slurry and the coalesence of those particles into agglomerates is carried out at a temperature in the range of 21.1°±6° C. 
     
     
       11. A process as defined in any of the preceding claims 1-3 wherein the raw coal is sub-bituminous and wherein a surfactant is mixed with said slurry prior to separation and agglomeration of the coal particles in an amount effective to generate on said coal particles apparent surfaces which are compatible with the agglomerant employed to effect said separation and agglomeration. 
     
     
       12. A low ash coal produced by a process as defined in any of the preceding claims 1-3. 
     
     
       13. A process for recovering coal as defined in claim 3 wherein the dispersion of the coal particles making up the agglomerates is effected by removing sufficient agglomerant from the mixture of agglomerates and aqueous liquid to reduce the concentration of agglomerant to 20-30 percent based upon the weight of the solids in the mixture. 
     
     
       14. A process as defined in claim 13 wherein the removal of the agglomerant is promoted by heating the mixture of agglomerates and aqueous liquid. 
     
     
       15. A process for recovering a partially oxidized or lower rank coal from a composite in which mineral matter is associated therewith, said process including the steps of: comminuting said composite in an aqueous liquid slurry until it is resolved into particles which are essentially coal and particles which are essentially mineral matter; effecting a separation of said coal particles from said mineral matter particles and a coalesence of the coal particles into agglomerates with an agglomerant which is capable of being adsorbed onto the surfaces of the coal particles to render them more hydrophobic without effecting the hydrophilicity of the mineral matter and of forming liquid bridges between the coal particles and which is selected from the group consisting of: 1,1,1-trichloro-1,2,2-trifluoroethane,   pentane,   trichlorofluoromethane, and   2-methylbutane; and recovering the agglomerates from the aqueous liquid, said process being characterized by the step of dispersing in said slurry an additive which is capable of increasing the adsorptivity of the surfaces of the coal particles with respect to said agglomerant.     
     
     
       16. A process as defined in claim 15 wherein the adsorptivity increasing additive is selected from that group of compounds having the formulas ROH, RNH 2 , R 2  NH, and R 3  N where R is an organic ring or an organic chain having more than four carbon atoms. 
     
     
       17. A process as defined in claim 15 wherein the adsorptivity increasing additive is a surfactant. 
     
     
       18. A process as defined in claim 7 which includes the step of adding to the aqueous liquid in which the composite of coal and mineral matter is comminuted at least one composition which is effective to increase the pH of the slurry of aqueous medium and composite. 
     
     
       19. A process as defined in claim 15 wherein the adsorptivity increasing additive is a Lewis base. 
     
     
       20. A process as defined in claim 1 wherein said liquid agglomerating agent is mixed with said slurry in an amount which is sufficient to essentially completely fill the voids between the particles making up the product coal agglomerates. 
     
     
       21. A process as defined in claim 20 wherein said liquid agglomerating agent is mixed with the diluted slurry in an amount ranging from 45 to 60 percent based on the dry weight of the coal in said slurry. 
     
     
       22. A process as defined in claim 1 wherein said liquid agglomerating agent is mixed with said slurry in an amount which is sufficient to form a stable, encapsulating monolayer film around each of the coal particles present in said slurry. 
     
     
       23. A process as defined in claim 2 wherein said slurry is diluted after the comminution of the composite in the liquid phase to a solids content of 1 to 14 weight percent. 
     
     
       24. A process as defined in claim 3 wherein, in the step of introducing the particles making up the first mentioned agglomerates into an aqueous liquid, the concentration of solids in the aqueous liquid is adjusted to a concentration in the range of 30 to 10 weight percent. 
     
     
       25. A process as defined in claim 3 wherein, in the step of reducing the concentration of agglomerant to a level sufficient to make a dispersion of the particles making up the agglomerates possible, said concentration is reduced to a level of 20 to 30 percent based on the weight of the solids in the slurry. 
     
     
       26. A process as defined in claim 15 wherein said adsorption increasing additive is mixed with said slurry in an amount that is sufficient to form a monolayer of the additive on the particles of coal in the slurry.